LOS ANGELES (AP) – The U.S. Department of Agriculture on Sunday recalled 143 million pounds of frozen beef from a Southern California slaughterhouse that is being investigated for mistreating cattle.

Officials said it was the largest beef recall in the United States, surpassing a 1999 ban of 35 million pounds of ready-to-eat meats.

The federal agency said the recall will affect beef products dating to Feb. 1, 2006, that came from Chino-based Westland/Hallmark Meat Co., which supplies meat to the federal school lunch program and to some major fast-food chains.

Secretary of Agriculture Ed Schafer said his department has evidence that Westland did not routinely contact its veterinarian when cattle became non-ambulatory after passing inspection, violating health regulations.

"Because the cattle did not receive complete and proper inspection, Food Safety and Inspection Service has determined them to be unfit for human food and the company is conducting a recall," Schafer said in a statement.

Federal officials suspended operations at Westland/Hallmark after an undercover video surfaced showing crippled and sick animals being shoved with forklifts.

Two former employees were charged Friday with animal cruelty. No charges have been filed against Westland, but an investigation by federal authorities continues.

Officials estimate that about 37 million pounds of the recalled beef went to school programs, but they believe most of the meat probably has already been eaten. There have been no reported illnesses linked to the beef at any of the schools.

"We don't know how much product is out there right now. We don't think there is a health hazard, but we do have to take this action," said Dr. Dick Raymond, USDA Undersecretary for Food Safety.

Federal regulations call for keeping downed cattle out of the food supply because they may pose a higher risk of contamination from E. coli, salmonella or mad cow disease because they typically wallow in feces and their immune systems are often weak.

About 150 school districts around the nation have stopped using ground beef from Hallmark Meat Packing Co., which is associated with Westland.